diff options
author | Manfred Spraul <manfred@colorfullife.com> | 2013-07-09 03:01:24 +0400 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2013-07-09 21:33:28 +0400 |
commit | f269f40ad5aeee229ed70044926f44318abe41ef (patch) | |
tree | 878fd6dabbf34c154809ed21f6d64cb90c7e394c | |
parent | 1a82e9e1d0f1b45f47a97c9e2349020536ff8987 (diff) | |
download | linux-f269f40ad5aeee229ed70044926f44318abe41ef.tar.xz |
ipc/sem.c: always use only one queue for alter operations
There are two places that can contain alter operations:
- the global queue: sma->pending_alter
- the per-semaphore queues: sma->sem_base[].pending_alter.
Since one of the queues must be processed first, this causes an odd
priorization of the wakeups: complex operations have priority over
simple ops.
The patch restores the behavior of linux <=3.0.9: The longest waiting
operation has the highest priority.
This is done by using only one queue:
- if there are complex ops, then sma->pending_alter is used.
- otherwise, the per-semaphore queues are used.
As a side effect, do_smart_update_queue() becomes much simpler: no more
goto logic.
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r-- | ipc/sem.c | 128 |
1 files changed, 88 insertions, 40 deletions
diff --git a/ipc/sem.c b/ipc/sem.c index 4d7f88cefada..6291257ee049 100644 --- a/ipc/sem.c +++ b/ipc/sem.c @@ -192,6 +192,53 @@ void __init sem_init (void) IPC_SEM_IDS, sysvipc_sem_proc_show); } +/** + * unmerge_queues - unmerge queues, if possible. + * @sma: semaphore array + * + * The function unmerges the wait queues if complex_count is 0. + * It must be called prior to dropping the global semaphore array lock. + */ +static void unmerge_queues(struct sem_array *sma) +{ + struct sem_queue *q, *tq; + + /* complex operations still around? */ + if (sma->complex_count) + return; + /* + * We will switch back to simple mode. + * Move all pending operation back into the per-semaphore + * queues. + */ + list_for_each_entry_safe(q, tq, &sma->pending_alter, list) { + struct sem *curr; + curr = &sma->sem_base[q->sops[0].sem_num]; + + list_add_tail(&q->list, &curr->pending_alter); + } + INIT_LIST_HEAD(&sma->pending_alter); +} + +/** + * merge_queues - Merge single semop queues into global queue + * @sma: semaphore array + * + * This function merges all per-semaphore queues into the global queue. + * It is necessary to achieve FIFO ordering for the pending single-sop + * operations when a multi-semop operation must sleep. + * Only the alter operations must be moved, the const operations can stay. + */ +static void merge_queues(struct sem_array *sma) +{ + int i; + for (i = 0; i < sma->sem_nsems; i++) { + struct sem *sem = sma->sem_base + i; + + list_splice_init(&sem->pending_alter, &sma->pending_alter); + } +} + /* * If the request contains only one semaphore operation, and there are * no complex transactions pending, lock only the semaphore involved. @@ -262,6 +309,7 @@ static inline int sem_lock(struct sem_array *sma, struct sembuf *sops, static inline void sem_unlock(struct sem_array *sma, int locknum) { if (locknum == -1) { + unmerge_queues(sma); ipc_unlock_object(&sma->sem_perm); } else { struct sem *sem = sma->sem_base + locknum; @@ -831,49 +879,38 @@ static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsop int otime, struct list_head *pt) { int i; - int progress; otime |= do_smart_wakeup_zero(sma, sops, nsops, pt); - progress = 1; -retry_global: - if (sma->complex_count) { - if (update_queue(sma, -1, pt)) { - progress = 1; - otime = 1; - sops = NULL; - } - } - if (!progress) - goto done; - - if (!sops) { - /* No semops; something special is going on. */ - for (i = 0; i < sma->sem_nsems; i++) { - if (update_queue(sma, i, pt)) { - otime = 1; - progress = 1; + if (!list_empty(&sma->pending_alter)) { + /* semaphore array uses the global queue - just process it. */ + otime |= update_queue(sma, -1, pt); + } else { + if (!sops) { + /* + * No sops, thus the modified semaphores are not + * known. Check all. + */ + for (i = 0; i < sma->sem_nsems; i++) + otime |= update_queue(sma, i, pt); + } else { + /* + * Check the semaphores that were increased: + * - No complex ops, thus all sleeping ops are + * decrease. + * - if we decreased the value, then any sleeping + * semaphore ops wont be able to run: If the + * previous value was too small, then the new + * value will be too small, too. + */ + for (i = 0; i < nsops; i++) { + if (sops[i].sem_op > 0) { + otime |= update_queue(sma, + sops[i].sem_num, pt); + } } } - goto done_checkretry; - } - - /* Check the semaphores that were modified. */ - for (i = 0; i < nsops; i++) { - if (sops[i].sem_op > 0 || - (sops[i].sem_op < 0 && - sma->sem_base[sops[i].sem_num].semval == 0)) - if (update_queue(sma, sops[i].sem_num, pt)) { - otime = 1; - progress = 1; - } - } -done_checkretry: - if (progress) { - progress = 0; - goto retry_global; } -done: if (otime) sma->sem_otime = get_seconds(); } @@ -1747,11 +1784,22 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops, struct sem *curr; curr = &sma->sem_base[sops->sem_num]; - if (alter) - list_add_tail(&queue.list, &curr->pending_alter); - else + if (alter) { + if (sma->complex_count) { + list_add_tail(&queue.list, + &sma->pending_alter); + } else { + + list_add_tail(&queue.list, + &curr->pending_alter); + } + } else { list_add_tail(&queue.list, &curr->pending_const); + } } else { + if (!sma->complex_count) + merge_queues(sma); + if (alter) list_add_tail(&queue.list, &sma->pending_alter); else |